Home - Hardware - GoMMC - Installation guide
GoMMC can be installed in a BBC model B, Master, B+ or Electron.
1) Take note of this picture of GoMMC's 10-pin configuration header (the one with the grey and blue jumpers on it). Its pins (in the orientation shown in the picture) are numbered :
| 9 | 10 |
| 7 | 8 |
| 5 | 6 |
| 3 | 4 |
| 1 | 2 |
So, in this example, there's a grey jumper on 3+4 and 9+10, and a blue one on 6+8 (note that all your jumpers will probably be black). The positions of the jumpers will differ depending on, among other things, what type of machine GoMMC is installed in.
2) Take note of the 'extras' that were supplied with your GoMMC :
3) Remember, after installation, to go to the 'Software updates' page here, download the .zip file containing the latest version of the GoMMC software, extract the 'Guide' text file, and carefully read the 'Basic' section.
Now skip ahead to 'BBC B installation', 'BBC Master installation', 'BBC B+ installation' or 'Electron installation', depending on which machine you have.
1) About the 'socket-to-wire-to-jumper' adapter (henceforth called 'the adapter') that came with your GoMMC. Only with the adapter installed, you can make use of the 'free ROM bank on GoMMC', which is like a 16 KB sideways RAM bank (except that its contents are remembered when the machine is switched off). If you already have sideways RAM banks in your machine that GoMMC can use to auto-load patched filing systems (refer to GoMMC's documentation), or you have an (E)PROM with a patched filing system permanently installed in your machine (again, refer to GoMMC's documentation), installing the adapter is not really necessary.
2) Note the numbers of the sideways ROM sockets in your machine. The sockets are located below the keyboard, on the righthand side of the machine. From the side of the machine inwards, the numbers are 15, 14, 13 and 12. The BASIC ROM is usually installed in socket 12.
Now skip ahead to 'BBC B installation with adapter' or 'BBC B installation without adapter' depending on whether or not you're installing the adapter.
You should now have something resembling this picture.
Ready.
There are really only two 'good' position combinations for GoMMC and the adapter socket. Both prevent the adapter wire (where it goes into the adapter socket) from shorting against the underside of the GoMMC PCB. The preferred combination is : GoMMC in 15, adapter in 12 (move the BASIC ROM to 13). The other combination is : GoMMC in 14, adapter in 15. The drawback of the latter combination is that you will not be able to '*Unplug' any patched filing system loaded into GoMMC's free ROM bank (but wiping the bank instead basically has the same effect).
You should now have something resembling this picture. Note and check the correct orientation of the adapter socket.
Ready.
1) About the plain IC socket (henceforth called 'the extra socket') that came with your GoMMC. You must mount this 'between' GoMMC and the sideways ROM socket in the Master, to gain extra height (else GoMMC will short against links LK19, LK18 and LK12 on the Master motherboard).
2) Note that GoMMC can only be installed in the 32K sideways ROM socket for slots 6+7, IC37, the first one 'south' of the MOS ROM. This is only because of physical constraints (in theory, GoMMC could also have been installed in the 32K sideways ROM socket for slots 4+5, IC41, the third one 'south' of the MOS ROM, although not in IC27, because it's a 16K-only slot).
3) Note that, if needed, you can regain the use of sideways RAM banks 6+7, but this requires a (solderless) modification. Refer to 'Regaining use of sideways RAM banks 6+7'.
Then :
You should now have something resembling this picture.
Now check your CPLD version. If you have a red sticker saying 'G 1.0x' (x is 2, 3 or 4 currently) on the big black chip in the brown socket on GoMMC, your GoMMC has CPLD version 1.0x. Else, you have the older CPLD version 1.00 or 1.01.
If you have a version 1.00 or 1.01 CPLD, you must continue with 'Additional BBC Master installation'. Otherwise :
Ready.
You have an old CPLD version. A flying wire (this is the 'thick-pin-to-wire-to-jumper' contraption supplied with older GoMMCs) must be fitted.
There are two installation options.
- Option 1 : like this.
Note that, for a better view, the plastic speaker holder has been removed. In reality, you will lay the flying wire 'over' the plastic holder.
1) Don't install (or remove) the jumper on pins 9+10 of GoMMC's configuration header.
2) Connect the thick pin side of the flying wire to the eighth pin (counting from the top of the picture), on the leftmost pin row, of the nearest cartridge socket. Stick the thick pin 'behind' the cartridge socket pin on the 'left' side. It should fix quite well when you push it home, but do this gently.
3) 'Hook' the jumper side of the flying wire to pin 10 of GoMMC's configuration header. Do not put the jumper over both pin 9 and 10, it should only be attached to pin 10.
Ready.
- Option 2 : like this.
(Do this only if you can trust yourself, or someone else who will do the work for you, with a soldering iron).
This is like option 1, but the second step becomes :
2) Desolder the thick pin from the flying wire, and solder the remaining short, tinned wire end to the 'west' leg of resistor R43 on the Master motherboard (1K, striped brown, black, red, the one just north of the 65C12). This is a much more reliable connection than via the cartridge socket.
Ready.
To regain the use of sideways RAM banks 6+7, which may be needed in some cases (e.g. to run the 'Master enhanced' versions of some games), proceed as follows. Note that you will lose the possibility to use both the free ROM bank on GoMMC, and the 'middle' of the three Master ROM sockets (IC27, ROM number 8, directly 'south' of the ROM socket that GoMMC is in).
1) Note that you need the 'special' version of GoMMC. The 'normal' version is unsuitable. Note, also, that you need to run the 'special' version of the GoMMC software (take care of always downloading e.g. 'gommc065s.zip' instead of 'gommc065.zip', both will be there, wherever the latter is).
2) Note the numbers of the sideways ROM sockets in your machine, and their corresponding 16K/32K selection links. Both sockets and links are located near the power supply (the selection links are closest to it). Looking from the keyboard side, from top to bottom, and from left to right, the sockets are :
Then :
Ready (no pictures, sorry).
1) Note that you have a separate 'GoMMC for Electron interface' plug-in card that is needed to interface GoMMC to your Electron. For orientation, always look at the side where the components are, holding the interface with the (green) Electron connector facing you. And take note of 'north', 'south', 'east' and 'west' (e.g. the Electron connector is now 'south').
2) Note that your GoMMC for Electron interface has two free IC sockets. The 32-pin (west) one is the 'utility' socket. The 28-pin (east) one is where you will install GoMMC.
3) Note the (only) jumper on your GoMMC for Electron interface (just east of the 28-pin socket). It is the ROM/SRAM jumper. It selects whether the utility socket contains a ROM or SRAM chip.
Then :
I.e. first you had something like this (an 8-bank SRAM has been installed in this case), and after installing GoMMC, you have something like this.
The utility socket on the GoMMC for Electron interface may remain empty. But it is meant to take a ROM or SRAM chip, providing up to 2 (for 28-pin chips) or 8 (for 32-pin chips) sideways ROM (if ROM) or RAM (if SRAM) banks. The chip must be suitable (e.g. it must have a standard JEDEC pinout, like a 27C1001 or 628128). If in doubt consult me ! If you install a ROM, the ROM/SRAM jumper must be set 'west', else 'east'. If you install a 28-pin chip, it must be 'lined up' to the south side of the 32-pin socket (i.e. the northmost 4 pins remain unoccupied). Consult the chapter entitled 'Sideways ROM/RAM' in the GoMMC Guide as well, before you put anything in the utility socket.
Now simply plug this 'combo' into your Electron's expansion port, at the back of the machine.
Ready.
